Combined heat and power generation (“CHP” or “cogen”) is the simultaneous generation of electricity and heat by a thermal power station. In particular, the typical power station includes one or more gas turbine engines that generate electricity and emit a certain amount of heat as a byproduct of generating electricity. CHP captures and uses some or all of the heat for heating hospitals, commercial buildings or various other buildings that are located geographically close to the power station. As another example, CHP can also be used for heating a district water supply.
Two common types of gas turbine engines may include those originally designed for industrial and power generation applications (“industrial machines”) and those typically derived from aeronautical engines (“aeroderivatives”). The former may have a heavy weight and robust construction for a long life with less frequent maintenance overhauls. The latter may start up, change loads and shut down more quickly than the industrial machines. Furthermore, aeroderivatives may have higher pressure ratios, higher efficiencies and lower exhaust temperatures than the industrial machines and thus may produce less steam in the combined cycle and CHP configuration. Potential obstacles to CHP can include matching heat and electric loads in quantity and timing as required by the power station.
Therefore, a need exists for a gas turbine engine that meets any heat load requirement by using a reheat combustor and a power turbine having a sufficient set of nozzle guide vanes (“NGVs”), or, alternatively if the heat load is variable, by using variable nozzle guide vanes (“VNGV”).